In the process for conventional stuffer box crimping, a continuous product of filamentary material (hereinafter referred to as a "tow") is passed through a pair of nip rolls which forcibly feed the tow into a confined passage from which its emergence is resisted so that the tow assumes a crimped or buckled form and is subjected to a substantial degree of pressure by subsequently entering portions of the tow thereby fixing the crimp and causing it to be retained in the tow subsequent to its emergence from the confined passage.
Representative apparatus for conventional stuffer box crimping is disclosed in U.S. Pat. Nos. 2,156,723; 2,693,008; 2,862,279 and 3,571,870.
Such apparatus generally comprises a pair of cylindrical feed rolls mounted to form a nip and a crimping chamber positioned in close proximity to the point where the tow exits from the nip. The crimping chamber conventionally comprises two oppositely positioned doctor blades maintained near or against the surface of the cylindrical feed rolls as they rotate past the nip point and forming the entrance to the chamber, two side or cheek plates to confine the lateral movement of the tow in the chamber and a confining means at the exit of the crimping chamber to provide resistance to the forward movement of the tow.
The confining means may be an adjustable positioned flap or gate as in the above mentioned U.S. Pat. No. 2,693,008 or may be the outer end of one of the doctor blades of the chamber which is pivotally mounted to permit an increase or decrease in the space between the blades at the exit end of the chamber as disclosed in the aforementioned U.S. Pat. Nos. 2,156,723; 2,862,279 and 3,571,870.
In the case of any of this apparatus, the nature of the crimp imparted to the strand is a function of the size of the crimping chamber and, in particular, the depth of the chamber which is determined by the distance which the doctor blades are positioned away from each other. When the doctor blades are positioned relatively close together, they form a shallow crimping chamber which will induce a multiplicity of small, relatively uniform crimps. When the doctor blades are positioned relatively far apart, they form a relatively large, or deep, crimping chamber which will produce predominantly large but also less uniform crimps in a tow. A relatively small crimping chamber would, therefore, usually be preferred for most crimping operations and particularly for those in which uniformity of crimp is of primary importance.
However, since the edges of the doctor blades forming the entrance to the crimping chamber must be maintained against or at least in close proximity with the cylindrical surfaces of the feed rolls, a shallow or small crimping chamber with the doctor blades relatively close together requires the use of relatively small feed rolls to avoid having to place the crimping chamber far into the nip of the feed rolls in order to obtain contact between the closely spaced apart doctor blades and the corresponding surfaces of the feed rolls.
The utilization of small feed rolls is not generally preferred in any feeding operation since the smaller feed rolls present a smaller surface area for wear, necessitate higher rotational speeds to obtain equivalent feed and, in the case of a crimping apparatus, make the installation and maintenance of the chamber side or cheek plates difficult. Therefore, a conventional small stuffer box crimper could be utilized with large feed rolls only by utilizing long, extremely narrow doctor blades which would fit deep into the nip of the two large diameter rolls. These doctor blades are difficult to produce and easily damaged. Furthermore, such a crimping chamber is difficult to position against the feed rolls because of the nature of the doctor blades but, moreover, because the entire chamber is ultimately positioned far in toward the nip of the rolls. This position additionally makes access to the chamber for servicing difficult. As a result, conventional stuffer box crimping apparatus generally utilizes cylindrical feed rolls which have a diameter equal to from about 15 to about 40 times the depth of the crimping chamber.
The foregoing discussion has centered on stuffer box crimpers having a crimping chamber in line with the bite of the feed rolls. Such conventional stuffer box crimpers crimp tow in what is best described as a stick-slip motion. Stuffer box crimping apparatus however, exists wherein the crimping chamber is offset with the bite of the feed rolls. Offset stuffer-box crimpers are known to reduce damage to the fiber being crimped and moreover to affect a high degree of uniformity in the crimped product. This improvement is at least partially due to preventing stick-slip motion in the crimping process. U.S. Pat. No. 2,917,784 for instance, discloses in FIG. 13 thereof a stuffer box crimper having an offset crimping chamber formed by a fixed curved doctor blade and a floating feed roll. Back pressure is provided by means of a pivoted flapper. The curved doctor blade is curved so that the cross-section of the crimping chamber is relieved away from its entrance by being tapered slightly outwardly in that direction, usually about two to six degrees. In other words, the depth of the crimping chamber increases toward the exit portion thereof. A second scrapper blade may optionally be used to remove the crimped tow from the floating roll.
U.S. Pat. No. 3,146,512 employs a conventional feed roll pair with a stuffer box offset from the bite thereof. The salient feature of U.S. Pat. No. 3,146,512 is the use of a grooved doctor blade which connects with a circumferential groove of an abutting wheel member. U.S. Pat. No. 3,146,512 does not disclose a rectangular cross-section crimping chamber, but rather relies upon an elongated crimping chamber having a unique cross-sectional configuration designed to trap and prevent premature release of filamentary material.
U.S. Pat. No. 3,441,988 employs a curved doctor blade which at least partially surrounds the external surface of a roller to produce a gap-forming segment or crimping chamber. Filaments are fed into the zone and their exit is restrained by a retarding means positioned at the exit of the zone. U.S. Pat. No. 3,441,988 however, cannot be construed as a stuffer-box crimper in the classic sense inasmuch as it does not crimp tow issuing from the bite of a feed roll pair.
None of the foregoing patents disclose a two roll feed system offset stuffer box crimper wherein yarn is set in the crimped configuration within a rectangular cross-section crimping chamber formed by means of a curved doctor blade which converges toward one of the feed rolls and wherein the cross-sectional area of the crimping chamber diminishes toward the exit portion thereof.